1. Technical Field
The present invention relates to an antenna feed structure for electrically connecting a rotatable antenna to a circuit on a circuit board, the connection being made with a feeding metallic part on the circuit board.
2. Background Art
FIG. 9 is a schematic view externally showing a card device in simplified form. A card device 41 comprises a card case 42, a circuit board 43 accommodated in the card case 42, and an antenna 44 rotatably disposed at the outer side of the card case 42 for being electrically connected to a circuit (not shown) formed on the circuit board 43.
An antenna rotary shaft 45 formed of a conductor is formed so as to protrude from one end of the antenna 44, and a through hole for inserting the antenna rotary shaft 45 into the card case 42 from outside the card case 42 is formed in a side wall of the card case 42. The antenna rotary shaft 45 is electrically connected to the circuit at the circuit board 43 by inserting the antenna rotary shaft 45 into the card case 42 through the through hole for inserting the antenna rotary shaft. As a result, the antenna 44 is electrically connected to the circuit on the circuit board 43 through the antenna rotary shaft 45.
Other antenna feed structures of background interest are described in Japanese Unexamined Patent Application Publication No. 2001-339211, and PCT Japanese Translation Patent Publication No. 11-504771.
The antenna rotary shaft 45 rotates. Therefore, due to various reasons arising from the rotation of the antenna rotary shaft 45, it is not desirable to directly connect the antenna rotary shaft 45 to the circuit board 43. Consequently, the use of a feeding metallic part such as a feeding metallic part 46 shown in a model diagram in FIG. 10 has been proposed. The feeding metallic part 46 electrically connects the antenna rotary shaft 45 to the circuit at the circuit board 43, so that the antenna rotary shaft 45 is not directly connected to the circuit board 43.
The entire feeding metallic part 46 is formed of a conductor. The feeding metallic part 46 comprises a mounting portion 47 for mounting to the circuit board 43, an antenna contact-and-connection portion 48 for contact and connection with the antenna rotary shaft 45, and an elastic supporting portion 49 for elastically supporting the antenna contact-and-connection portion 48 at the mounting portion 47. The elastic supporting portion 49 possesses elasticity (springiness) allowing biasing force to be produced from the antenna contact-and-connection portion 48 towards the antenna rotary shaft 45.
The mounting portion 47 of the feeding metallic part 46 is electrically connected to the circuit on the circuit board 43. By bringing the antenna rotary shaft 45 into press-contact with the antenna contact-and-connection portion 48 of the feeding metallic part 46, they are electrically connected together. This causes the antenna 44 to be electrically connected to the circuit on the circuit board 43 through the antenna rotary shaft 45 and the feeding metallic part 46.
Accordingly, when the feeding metallic part 46 shown in FIG. 10 is used, the antenna 44 is electrically connected to the circuit on the circuit board 43 without directly connecting the antenna rotary shaft 45 to the circuit board 43. However, when the feeding metallic part 46 shown in FIG. 10 is used, the following problems arise.
Whereas an end surface of the antenna rotary shaft 45 is spherical, a portion of contact of the antenna contact-and-connection portion 48 of the feeding metallic part 46 with the antenna rotary shaft is planar. Therefore, the antenna rotary shaft 45 and the antenna contact-and-connection portion 48 of the feeding metallic part 46 are in point contact with each other, as a result of which the area of contact is very small. In addition, since the antenna rotary shaft 45 tends to swing due to the rotation of the antenna 44, when the antenna 44 rotates, the location of contact of the antenna contact-and-connection portion 48 of the feeding metallic part 46 with the antenna rotary shaft 45 tends to vary. These two problems, that is, the problem of the area of contact between the antenna rotary shaft 45 and the antenna contact-and-connection portion 48 being small and the problem of the location of contact of the antenna contact-and-connection portion 48 with the antenna rotary shaft 45 varying, make it difficult to provide stable contact and electrical connection between the antenna rotary shaft 45 and the antenna contact-and-connection portion 48 (that is, stably electrically connect the antenna 44 and the circuit on the circuit board 43).
Further, the distance between the circuit board 43 and the antenna rotary shaft 45 is determined by various factors. Because allowance must be made for the distance between the circuit board 43 and the antenna rotary shaft 45, the design of the feeding metallic part 46 cannot be carried out with much freedom. When one tries to vary the contact pressure between the antenna rotary shaft 45 and the antenna contact-and-connection portion 48 of the feeding metallic part 46, the design of the feeding metallic part 46 is changed, for example, to vary the location where the feeding metallic part 46 is mounted to the circuit board 43 or to vary the elastic force of the elastic supporting portion 49 of the feeding metallic part 46. However, since the distance between the circuit board 43 and the antenna rotary shaft 45 is small, a range in which the mounting location of the feeding metallic part 46 can be moved is small. Therefore, the contact pressure between the antenna rotary shaft 45 and the antenna contact-and-connection portion 48 substantially cannot be adjusted by adjusting the mounting location of the feeding metallic part 46. Still further, since the feeding metallic part 46 is designed considering various factors, such as material costs and manufacturing process, the feeding metallic part 46 is designed under many constraints. Therefore, it is difficult to change the design for varying the elastic force of the elastic supporting portion 49. Consequently, the structure of the feeding metallic part 46 shown in FIG. 10 has the problem that it is difficult to adjust the contact pressure between the antenna rotary shaft 45 and the antenna contact-and-connection portion 48 of the feeding metallic part 46.